This invention relates to the field of alternators, and more particularly, this invention relates to the field of regulating an alternator charging system.
In an automobile system, an alternator charging system maintains a substantially constant battery voltage and usually includes an alternator with voltage regulator and a rectifier bridge. The alternator supplies the energy to the battery for recharging the battery and is typically proportional to the current flow through its field windings at a given alternator RPM. The voltage regulator controls the output of an alternator in accordance with the voltage level of the battery by controlling the current flow through the field windings of the alternator. The voltage regulator senses when the battery voltage drops below a specified voltage level and applies current to the field windings of the alternator thereby providing the charging current from the alternator to the battery. After the battery voltages reach a desired voltage level, the voltage regulator stops current flow to the field windings and terminates the charging. A pulse width modulated (PWM) control algorithm can be used and actually does not stop current flow by the inductive nature of the field windings. When the voltage is applied to a field winding, the current ramps up and when the voltage is removed, the current ramps down. In a PWM situation, the current is constantly ramping up and down at a much slower rate than the frequency of the PWM duty cycle. This makes for a fairly constant current in the field windings. The level of this current is determined by the rotational speed of the field rotor, the loading on the alternator, and the desired voltage the regulator is trying to regulate at.
As is well known to those skilled in the art, the amount of voltage level at which the battery is charged depends on the battery temperature. At low temperatures, the battery only has to be charged at a lower voltage and can handle more charging current as compared to hotter temperatures. Some voltage regulators, such as used with General Motors and Ford vehicles, use integral temperature sensors that provide feedback to approximate the temperature of the battery and account for different temperatures of the battery. Most regulators are commonly formed integral with the alternator and operate at the temperature of the alternator and this system is commonly used to reflect battery temperature.
One type of microcomputer controlled electronic alternator for automobiles is disclosed in U.S. Pat. No. 4,659,977, assigned to Chrysler Motor Corporation, the disclosure which is hereby incorporated by reference in its entirety. This system uses the microcomputer intelligence for controlling engine operation to improve the charging system. This type of system eliminates a conventional voltage regulator. The microcomputer senses when a vehicle decelerates and charges the battery to a high voltage level during the periods of deceleration, thus using some of the momentum of the vehicle that is usually wasted in the converted form of vehicle breaking and heat. The additional load placed on the engine assists in slowing the vehicle. However, the system uses the main engine controller and processor. There are also hybrid regulators on the market that can be programmed by a hybrid resistor change. One drawback of this type of system is that they are limited to a one slope system and must be set at the construction of the regulator.
Other designs have used mask level programming for different alternator charging systems and regulators. These were complex and required difficult circuits to manufacture and complicated digital and analog circuits. Also, because of a unique mask that may have been generated for a unique alternator arrangement, different regulators were required. Slope programming had also been limited to mask level programming.
It is therefore an object of the present invention to provide a programmable alternator charging system that is adaptable for different alternator charging systems based on the specific alternator charging system requirements of an alternator.
The present invention is advantageous and provides a programmable temperature compensation slope for an automotive charging system regulator. In the prior art, as noted before, slope programmability was limited to mask level programming. Mask level programming required layout changes, new mask sets to be generated, and time for this effort as well as to fabricate the new devices.
The implementation of multiple slopes required new band gap circuits for each slope used. The complexity of charging system regulation has increased to where new and multiple slope temperature compensation is becoming the norm. The programmable system of the present invention is performed digitally.
In accordance with the present invention, the system and method regulates an alternator charging system and includes a memory for storing the regulating voltages used at specific temperatures for the specific alternator charging system requirements of an alternator. The memory can typically be formed as a nonvolatile memory, such as a semiconductor circuit memory that can be programmed for the specific alternator charging system requirements of an alternator.
A circuit generates a digital signal indicative of both the temperature of a battery supplied by the alternator charging system and the charging system voltage. A digital comparator receives the digital signal and compares the digital signal with the regulating voltage stored within the memory for the specific temperature indicative of the temperature of the battery supplied by the alternator charging system and generates a regulator control signal that is fed to a regulation control loop of the alternator charging system.
In accordance with the present invention, a temperature measuring circuit as part of the regulator can measure the temperature of the battery supplied by the alternator charging system and generate an analog temperature signal corresponding to the measured temperature. A multiplexer receives the analog temperature signal and the analog signal indicative of the charging system voltage and multiplexes the two signals into a multiplexed signal. An analog-to-digital converter converts the multiplexed signal into a digital signal. An n-bit latch receives the digital signal. The n-bit latch can comprise an 8-bit latch. An error amplifier circuit can receive and amplify an analog signal indicative of the charging system voltage.
A method is also disclosed and comprises the steps of storing in a memory the regulating voltages used at specific temperatures for the specific alternator charging system requirements of an alternator. A digital signal is generated indicative of the temperature of a battery supplied by the alternator charging system and a charging system voltage. This digital signal is digitally compared with the regulating voltage stored within the nonvolatile memory for the specific temperature and is indicative of the temperature of a battery supplied by the alternator charging system.